(a) Technical Field of the Invention
The present invention relates to a park-position mechanism for an engine, and in particular to a mechanism for enhancing operation smoothness for switching to a park position.
(b) Description of the Prior Art
As shown in FIG. 1 of the attached drawings, an all-terrain vehicle (ATV), generally designated with reference numeral 1, comprises a vehicle frame 11, a steering mechanism 12, front wheels 13, a seat section 14, rear wheels 15, a power unit 2 that provides mechanical power for driving the all-terrain vehicle 1. The steering mechanism 12 is mounted in a way which, allows for rotation to a front end of the frame 1 and the front wheels 13 are mounted at a lower portion of the steering mechanism 12. The seat section 14 is arranged on a top side of the frame 11 behind the steering mechanism 12. The power unit 2 is arranged below the seat section 14.
The power unit 2, as shown in FIG. 2 of the attached drawings comprises an engine system 21 and a stepless transmission system 22 that is driven by the engine system 21. The stepless transmission system 22 is coupled to a rear wheel axle 24 by a chain 23 to drive the rear wheels 15 that are attached to the rear wheel axle 24.
Switching between forward and reversed movements of the all-terrain vehicle 1 is done with a selector mechanism 3. A conventional selector mechanism 3 is shown in FIGS. 2 and 3 of the attached drawings, comprising a selector rod 31 that has a gear 311 mating a gear 321 mounted on a selector hub shaft 32. The selector huh shaft 32 supports a selector hub 322 that is axially movable along the shaft 32. Position-selection slots (not labeled) are formed on the selector hub 322 for defining positions of the selector mechanism 3, such as a “DRIVE” position, a “NEUTRAL” position, a “REVERSE” position, and a “PARK” position.
A shaft 33 carries a fork 331 having an end engaging the position-selection slots of the selector hub 322 and an opposite end engaging a slide block 341 mounted on a main shaft 34. The slide block 341 is axially movable along the main shaft 34. A forward gear 342 and a reversing gear 343 are mounted to opposite sides of the slide block 341. The reversing gear 343 is coupled to a reversing shaft 344 and the reversing shaft 344 supports a switching gear 345 located on an opposite end. The switching gear 345 is coupled to a driven shaft 221 of the stepless transmission system 22.
The main shaft 34 is coupled to a gear 3461 of an output shaft 346. An output toothed wheel 3462 is mounted to an outer end of the output shaft 346 and is coupled to the rear wheels 15 by the chain 23.
As shown in FIG. 2, when, the engine system 21 is started, the power generated by the combustion of fuel inside a combustion chamber 211 of the engine system 21 causes a piston 212 to do reciprocal movement, which in turn rotates a crankshaft 213. A drive pulley 221 that is mounted to the crankshaft 213 is synchronously rotated with the crankshaft 213 and in turn drives a driven pulley 222 of the stepless transmission system 22, which in turn rotates a driven shaft 224 through a clutch 223. The driven shaft 224 drives the forward gear 342 and also rotates the reversing gear 343 through the switching gear 345 and the reversing shaft 344.
With reference to FIGS. 1-3, to select the DRIVE position, an operation lever 30 is manually moved fern an “N” position, to a “D” position, which moves the selector rod 31 and the gear 311 of the selector rod 31 in turn drives the gear 321 of the selector hub shaft 32 to rotate the selector huh 322. The fork 331 is thus forcibly moved along the position-selection slot of the selector hub 322 toward the DRIVE position. At the same time, the selector hub 322 is forcibly moved rightward to contract a compression spring 324 in the rightward direction. The opposite end of the fork 331 simultaneously drives the slide block 341 to move leftward along the main shaft 34, whereby the slide block 341 engages holes 3421 defined in the forward gear 342, causing the forward gear 342 to rotate the main shaft 34. The main shaft 34 then drives the gear 3461 to synchronously rotate the output shaft 346, which in turn drives a toothed wheel 241 mounted to the rear wheel axle 24 for rotating die rear wheel axle 24 in the direction for driving the all-terrain vehicle 1 forward.
To reverse the all-terrain vehicle 1, the operation lever 30 is manually switched to an “R” position, which in turn moves the selector lever 31 to cause the gear 311 of the selector lever 31 to drive fee gear 321 of the selector hub shaft 32 for rotating the selector hub 322. The fork 331 is then caused to move along the position-selection slot of the selector huh 322 to the REVERSE position, and at the same time, the selector hub 322 is forcibly moved leftward to contract a compression spring in the leftward direction. The opposite end of the fork 331 simultaneously drives the slide block 341 to move rightward along the main shaft 34, whereby the slide block 341 engages holes 3431 defined in the reversing gear 343, causing the reversing gear 343 to rotate the main shaft 34, which in turn causes the toothed wheel 241 of the rear wheel axle 24 to rotate in the direction for reversing the all-terrain vehicle 1 via the chain 23.
To park the all-terrain vehicle 1 in a stable stop condition, the selector mechanism 3 is also provided with a PARK position, which as shown in FIGS. 3-5, is comprised of a cam 323 mounted on the selector hub shaft 32 by the selector hub 322 and a park gear 347 arranged on the main shaft 34 at a position corresponding to the cam 323. A park arm 4 is arranged between the cam 323 and the park gear 347 and has opposite ends forming projections 41,42 respectively engageable with the cam 323 and the park gear 347.
The park arm 4 forms a holed base 43 that is rotates and fits over a stud 44. The stud 44 is fixed on a crankshaft case 2a to server as a rotational axis of the park arm 4, whereby the park arm 4 is rockable about the stud 44.
When the operation lever 30 is switched to a “P” position, the selector lever 31 moves the gear 311 to cause displacement of the selector hub 322 whereby the cam 323 by the selector hub 322 forces the projection 41 of the park arm 4 upward and simultaneously the projection 42 on the opposite side of the park arm 4 is driven downward to engage a deddendum trough 347 between adjacent teeth of the park gear 347 so as to fix the main shaft 34, thereby securing the main shaft 34 and the rear wheels 15 and making the all-terrain vehicle 1 in a stable parking condition.
Although effective in securing the main shaft 34 and the rear wheels 15 in a parked condition, the conventional mechanism suffers certain drawbacks. For example, and as shown in FIG. 5, when the projection 41 of the park arm 4 is moved upward by the cam 323, and the opposite projection 42 is simultaneously driven downward, due to the width of fee teeth of the park gear 347, the projection 42, during its downward movement, may accidentally get into contact with an addendum top face 347b of a tooth of the park gear 347, whereby the projection 42 cannot move into the trough 347a until the main shaft 34 and thus the park gear 347 make a further rotation to align the trough 347a with the projection 42. During the period when the projection 42 is in contact with the top face 347b of the tooth of the park gear 347, the projection 41 of the park arm 4 is continuously forced upward by the cam 323, which causes operation trouble in switching to the PARK position.
Further, the trouble that the projection 42 is prevented from lowering into the tooth trough 347a by the top face 347b while the projection 41 is continuously moved upward induces undesired strains in the park arm 4, which may eventually damage the park arm 4.
Thus, it is desired to provide a park-position mechanism that allows for smooth position switching and protects the mechanism itself for endured service life.